The present invention relates to mechanically strong, water-disintegrable agglomerates containing various particulate calcium sources for use as a soil conditioner to neutralize soil acidity and provide a source of nutrient values. The present invention also relates to processes for forming such agglomerates as well as to methods of introducing nutrient values into cultivated soil so as to inhibit leaching of the nutrient values and improve utilization of the nutrient values by plants grown in the soil.
Soil conditioners or liming agents are widely used in agriculture, lawn care and gardening to reduce soil acidity and promote plant health. A variety of calcium-containing materials, in particulate or granulated form, are used as soil liming agents. Conventional liming agents include: limestone, dolomitic limestone, lime, slaked or hydrated lime, and gypsum.
Many industrial processes produce waste solids containing calcium. For example, the manufacture of cement and lime is accompanied by the generation of large quantities of dust collected from the hot gaseous effluents vented from the kiln. Similar calcium-containing dusts are recovered from the stack gases and ash residues produced during the burning of manure fuels (i.e., manure ash). These particulate wastes share two properties that make them potentially useful for application to cultivated soils: (1) significant acid neutralization capacity; and (2) high concentrations of calcium and other important soil nutrients such as potassium and sulfur. It has been suggested to use calcium-containing waste solids such as cement kiln dust to lime cultivated soil (See T. A. Davis, et al., xe2x80x9cDisposal and Utilization of Waste Kiln Dust From Cement Industryxe2x80x9d, EPA Report No. 670/2-75-043 (May 1975)) as a way of reclaiming these sizeable waste streams. However, expanded agricultural-utilization of these waste products has been hindered by problems associated with storage, handling and application of these finely divided materials to soils. Raw cement kiln dust exiting the kiln, for example, is extremely fine, typically consisting of particles having an average particle size much less than 100 xcexcm, with a large portion of particles often having a particle size of 10 xcexcm or less. As a result, the dust is easily carried away by the wind and is difficult to bulk-blend with other materials in preparing various fertilizer formulations. Furthermore, modern fertilizer application equipment for broadcast or row placement of solid fertilizers, is designed for handling free-flowing, granular or pelletized materials having an appreciable mean diameter, not dust. Consequently, numerous problems are encountered when such equipment is employed for field application of finely-divided dust.
It would be highly beneficial to develop a process for granulating or agglomerating cement kiln dust and similar calcium-containing waste materials capable of consistently producing a mechanically strong soil conditioning agglomerate that readily disintegrates when contacted with water. In addition, it would be advantageous to improve the efficacy of agricultural liming agents generally and provide agglomerate compositions for introducing nutrient values into cultivated soil so as to inhibit leaching of the nutrient values and improve utilization of the nutrient values by plants grown in the soil.
Among the objects of the present invention, therefore, are the provision of a process for forming an agglomerate comprising calcium-containing waste materials such as cement kiln dust for use as a soil conditioning agent; the provision of such a process capable of producing an agglomerate having sufficient mechanical strength to withstand the rigors of handling, transport and application without excessive dusting; the provision of such a process which produces an agglomerate which disintegrates readily into particles having substantially the same size as the raw materials used to form the agglomerate once the agglomerate is incorporated into soil and exposed to water so that the various beneficial components of the agglomerate may be rapidly utilized by plants grown in the soil; and the provision of soil conditioning agents and agglomerate compositions made from calcium-containing waste materials as well as from conventional agricultural liming materials combined with plant nutrient values exhibiting improved efficacy.
Briefly, therefore, the present invention is directed to a process for forming an agglomerate for use as a soil conditioning agent. The process comprises preparing a preagglomerate containing a water-soluble binder and a particulate calcium source. The particulate calcium source has a particle size distribution such that less than about 1% by weight of the particulate calcium source is +20 mesh, less than about 10% by weight of the particulate calcium source is xe2x88x9220 +100 mesh and less than about 25% by weight of the particulate calcium source is xe2x88x92100 +200 mesh Tyler Standard Sieve Series. The preagglomerate-is pelletized to form the agglomerate. In accordance with another embodiment, the preagglomerate additionally contains a primary plant nutrient source and the particulate calcium source has a particle size distribution such that at least about 90% by weight of the particulate calcium source is xe2x88x92250 mesh Tyler Standard Sieve Series.
The present invention is further directed to an agglomerate for use as a soil conditioner and to provide a source of nutrient values. The agglomerate is formed by pelletizing a preagglomerate containing a particulate calcium source, a primary plant nutrient source and a water-soluble binder. The proportions of the particulate calcium source and the primary plant nutrient source in the preagglomerate are sufficient such that the agglomerate comprises about 15% to about 60% by weight of the particulate calcium source and about 30% to about 80% by weight of the primary plant nutrient source. The particulate calcium source has a particle size distribution such that at least about 90% by weight of the particulate calcium source is xe2x88x92250 mesh Tyler Standard Sieve Series. The agglomerate having a size ranging from xe2x88x927 to +8 Tyler Standard Sieve Series exhibits an average green crush strength of at least about 2 pounds.
The present invention is also directed to a method for introducing nutrient values into cultivated soil so as to inhibit leaching of the nutrient values from the soil and improve utilization of the nutrient values by plants grown in the soil. The method comprises applying to the soil an agglomerate comprising about 15% to about 60% by weight of a particulate calcium source, about 30% to about 80% by weight of a primary plant nutrient source and a water-soluble binder. The particulate calcium source exhibits a calcium carbonate equivalent value in excess of about 85% and has a particle size distribution such that at least about 90% by weight of the particulate calcium source is xe2x88x92250 mesh Tyler Standard Sieve Series. The agglomerate readily dissolves upon exposure to water to disintegrate into particles of the particulate calcium source and primary plant nutrient source.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.